Guardiola did not say how long he expects Haaland will be sidelined and says City will monitor the situation “week-by-week, day-by-day”.
“[It is] a bone stress reaction in his foot,” said Guardiola before the game at Kenilworth Road. After the last game against Aston Villa he felt like this and he can't play."
“I don't know [how bad it is]. Week by week, day by day, we will see what happens.”
City face Red Star Belgrade in a Champions League dead-rubber on Wednesday and Red Star Belgrade seems certain to miss that game at the Etihad Stadium.
Guardiola’s side then play Crystal Palace at the Etihad Stadium next Saturday in what is their last Premier League fixture until after Christmas.
They then travel to Saudi Arabia for the Club World Cup.
Their first game after Christmas is away at Everton on December 27.
Haaland had started in every Premier League game for City this season and is the top scorer in the division with 14 goals.
Without him Julian Alvarez started front against Luton.
Guaridola insisted his team had to adapt without Haaland.
“Erling has been so important since he’s arrived that’s for sure. But during the season we see this sort of thing. Injuries, suspensions, problems, we have to adapt,” he said.